Tag: sequenced

Meet “Inuk”. He is the ninth human to have their entire genome sequenced but unlike the previous eight, he has been dead for some 4,000 years old. Even so, DNA samples from a tuft of his frozen hair have revealed much about his appearance and his ancestry.

Inuk had brown eyes and brown skin. His blood type was A+. His hair was thick and dark but had he lived, he might not have kept it – his genes reveal a high risk of baldness. Inuk may well have died quite young. Like many Asians and Native Americans, his front teeth were “shovel-graded”, meaning that their back faces had ridged sides and concave middles. We even know about his earwax – it was dry, again like many Asians and Native Americans, rather than the wet wax that dominates other ethnic groups.

Inuk is the singular of Inuit and it means “man”. He was one of the Saqqaq people, one of the first cultures to settle in the frozen north of the New World. Few of their remains have been found – all we have are four small tufts of hair and four small pieces of bone. So Inuk’s genome is a treasure trove of knowledge about this extinct Eskimo culture. His remains were discovered in Greenland in the 1980s and his genome has just been sequenced by a large team of scientists from 8 countries, led by Morten Rasmussen, Yingrui Li and Stinus Lindgreen.

This isn’t the first time that scientists have tried to sequence the genes of an ancient human (or related species). So far, the most successful result was a first draft of the Neanderthal genome based on bone and tooth samples. It comprises just 63% of the total genome, but even getting this much was a struggle. Ancient genomes aren’t easy to decipher. Even if enough tissue is preserved, it is often riddled with the DNA of fungi and bacteria. The very act of extracting the tissues often adds human DNA to the list of contaminants.

Scientists have developed ingenious workarounds to this problem, but Rasmussen’s team solved it by working with a well-frozen specimen and focusing on his hair. Hair is a rich source of DNA and it protects genomes from both damaging elements and contaminating microbes. It allowed scientists to sequence the genome of the woolly mammoth and it has now done the same for Inuk. Around 80% of the DNA recovered from a tuft was Inuk’s hair was human, with no evidence of modern contamination. After all, all the scientists who handled the samples were European and there weren’t any traces of European sequences in the deciphered genome.

Rasmussen’s group used next-generation sequencing technology to analyse the recovered DNA. These powerful techniques allowed them to sequence around 80% of the genome around 20 times. With such extensive coverage, they could be incredibly confident about exactly which sequences lay in each location. Eske Willerslev who headed the group says, “It’s comparable to a modern human genome in terms of quality.” For comparison, the Human Genome Project’s gold standard required that the entire genome should be sequenced just 10 times.